For a certain project I had created a number of photometric catalogs, each one corresponding to a specific observing field. I would like to construct the final (merged) one but for this I needed to add a unique source identifier at the beginning of each row. I decided to create a F#-**** tag for each source with “F#” corresponding to the field id and **** to a counter for each source per field. The final command was:

for i in {1,2,4,5,6,7,8,9,10,11,12,13,16};do echo F$;awk -v id="$i" 'FNR>1 {print "F"id"-"1+c++, $0}' F$ >> results.tmp; done

So the command reads all the specific numbers for which a catalog with a filename of F* exists. The number of each field ($i) is parsed as an external variable (id) to awk which places it as the unique identifier “Fid-counter” with the incremental “counter” (1+c++) corresponding actually to the number of row (1+counter to begin from 1 instead of 0 – FNR avoids the first line of each catalog which is a column description). All results are written appended to the output file results.tmp (created automatically when non-existing).

Then, we can use sed to add the header:

sed -i '1i\#SourceID ...' results.tmp

An amazing drawing of Saturn

By grigoris | Filed in Astronomy

In the era of imaging even from our cell phones making a drawing of a planet seems redundant. However, this is certainly a different perspective of a direct experience at the eyepiece of a telescope. And the final result can be fascinating, such as this drawing from Paul G. Abel, using the Clark telescope (a 24″ refractor) at Lowell observatory.

A drawing of Saturn using the 24" Clark refractor at Lowell observatory (Paul G. Abel).

A drawing of Saturn using the 24″ Clark refractor at Lowell observatory (Paul G. Abel).

Source: ALPO-Japan

Building an observatory in Syria

By grigoris | Filed in Astronomy

At the last issue of CAP journal (No. 23, Feb 2018) we find the article “The World at a Glance: Highlights from IAU National Outreach Contacts” that provides short news from the IAU National Outreach Contacts. And for Syria we read:

“Mohamad AlAssiry: Despite the political situation, the Syrian Astronomical Association was building an observatory and opened in August 2017.”

which I found impressive given the country’s situation since the war broke out in 2011.

Of course, a counter-argument would criticize the prioritization given the number of lives threaten everyday in Syria. However, only education and civilization will help us overcome (on the long-term unfortunately…) these problems.

Finally, after some years of work, it has been accepted for publication in MNRAS.

Resolving the kinematics of the disks around Galactic B[e] supergiants

Grigoris Maravelias, Michaela Kraus, Lydia S. Cidale, Marcelo Borges Fernandes, Maria L. Arias, Michel Curé, Georgios Vasilopoulos

B[e] Supergiants are luminous evolved massive stars. The mass-loss during this phase creates a complex circumstellar environment with atomic, molecular, and dusty regions usually found in rings or disk-like structures. For a better comprehension of the mechanisms behind the formation of these rings, detailed knowledge about their structure and dynamics is essential. To address that, we obtained high-resolution optical and near-infrared spectra for 8 selected Galactic B[e] Supergiants, for which CO emission has been detected. Assuming Keplerian rotation for the disk, we combine the kinematics obtained from the CO bands in the near-IR with those obtained by fitting the forbidden emission [OI] λ5577, [OI] λλ6300,6363, and [CaII] λλ7291,7323 lines in the optical to probe the disk structure. We find that the emission originates from multiple ring structures around all B[e] Supergiants, with each one of them displaying a unique combination of rings regardless of whether the object is part of a binary system. The confirmed binaries display spectroscopic variations of their line intensities and profiles as well as photometric variability, whereas the ring structures around the single stars are stable. 1807.00796

Figure 12 from the paper: A cartoon illustration of the disk-structures as derived from our analysis. We represent the [OI] λ5577 line as *[OI]*, the [OI] λλ6300, 6363 doublet as [OI], and the [CaII] λλ7291, 7323 as [CaII]. The arrows above the rings symbolize the typical ring-widths and are given in km/s. (For more details on the data used and references see Table 3. Note that the relative structures and sizes are not in scale.

Catching a supernova just before it happens

By grigoris | Filed in Astronomy

Victor Buso is a really very lucky man! On September 20, 2016 we wanted to test his new camera mounted on a 40-cm Newtonian telescope. He pointed to the spiral galaxy NGC 613 because it was at that time located near the zenith. He took a series of 20s exposures spanning approximately an hour and a half. During the first part (about 40 exposures) there was no sign of anything unusual. After a break of 45 min though the exposures that he took revealed the rise of a supernova (SN 2016gkg). He is the first person to ever achieve that, ie. to capture the rise of a supernova just before its maximum light!

These observations are an unprecedented set of data for supernova physics. According to the recent paper by Bersten et al (incl. Buso) 2018 the data shows the clear presence of the shock breakout phase in the optical, i.e. the phase associated with the propagation of the radiation shock inside the star and its dissolution at the surface (Waxman & Katz 2016). This lasts seconds to a fraction of an hour typically, unless there is enough circumstellar mater ejected from the progenitor star before the supernova explosion then this phase may extend to days. The phase produces bright X-ray/UV flash but its optical manifestation has not been observed. So these observations show that the optical light curve is characterized by an extremely rapid brightening at relatively low luminosity.

What I find very critical in this work is actually how quick-witted Buso was. He is an amateur astronomer that didn’t just take the images. Instead he properly reduced them and he noticed the difference. The next important step was to communicate this to the appropriate channels that allowed for follow-up observations to be obtained in in less than a day later (including Swift X-ray, UV and optical telescopes, see Bersten et al 2018 for a list).

Bersten et al, 2018, Nature, 554, 497 (NASA/ADS link)
Waxman & Katz, 2016, arXiv:1607.01293 (arXiv link)

Skinakas return!

By grigoris | Filed in Astronomy

Yesterday was the first night that I found myself at Skinakas Observatory. Even though some years have passed, there are really minor changes. The mountain welcomed us with great weather (scarce clouds, humidity close to 50%, and almost no wind at all!), while the seeing proved to be really good (~1″).

The 1.3m Skinakas telescope.

Mixing a transient object with … Mars!

By grigoris | Filed in Astronomy

In the Astronomer’s Telegram #11448 [1] it is announced that a very bright (almost 1st magnitude) transient object is found between the Lagoon and the Trifid nebulae. No other object has been found in the region and the source itself was not visible some days earlier.

Within less than an hour later a second follow up telegram (#11449) informs the community that the transient object is … Mars !

It goes without saying that errors are for humans. But this one shows that every astronomer has to have a basic grasp of the night sky at least.


Seminar talk at NOA

By grigoris | Filed in Astronomy

As I am waiting my flight to Heraklion, I thought that I should post the talk that I gave earlier today at the National Observatory of Athens, Greece:

“B[e] Supergiants: a missing part from the massive star puzzle?”

Massive stars affect strongly the insterstellar medium through their intense stellar winds and their rich chemically processed material as they evolve. This interaction becomes substantial in short-lived transition phases of massive stars (e.g. B[e] Supergiants, Luminous Blue Variables, Yellow Hypergiants) in which mass-loss is more enhanced and usually eruptive. Consequently, a complex environment, combining atomic, molecular and dust regions is formed around these stars. In particular, the circumstellar environment of B[e] Supergiants is not well understood. Moreover, their possible link to other phases has not been fully uncovered yet, which is crucial given the importance of massive stars for Stellar Astrophysics and their influence on their host galaxies. Starting from an observational point of view, I will provide an overview of the B[e] Supergiant population and discuss the latest results.


Proposal brainstorming …

By grigoris | Filed in Astronomy

From our previous meeting.

Putting ideas on the chalkboard (Image © Paul Sell, CC BY-SA-ND).

During the last few days I have struggled a bit with the wavelength calibration of some long-slit spectra. When using the identify task of IRAF I found that I could select (“m”ark) only some of the lines, without any clear indication why the rest were not recognized (some were indeed stronger but others were equal or weaker). The actual error that kept popping out was “Center not found: check cursor position”. Although I went on to investigate all parameters (even the aidpars !) the one thing that solved the problem was finally to increase a bit the full-width of the features to be identified (fwidth), from the default value of 4.0 to 10 pixels. Apparently some of the lines seems too wide to be determined as real features by the task.